The next ‘Big One’ for the Bay Area may be a cluster of major quakes

A cluster of closely timed earthquakes over 100 years in the 17th and 18th centuries released as much accumulated stress on San Francisco Bay Area’s major faults as the Great 1906 San Francisco earthquake, suggesting two possible scenarios for the next “Big One” for the region, according to new research published by the Bulletin of the Seismological Society of America (BSSA).

“The plates are moving,” said David Schwartz, a geologist with the U.S. Geological Survey and co-author of the study. “The stress is re-accumulating, and all of these faults have to catch up. How are they going to catch up?”

The San Francisco Bay Region (SFBR) is considered within the boundary between the Pacific and North American plates. Energy released during its earthquake cycle occurs along the region’s principal faults: the San Andreas, San Gregorio, Calaveras, Hayward-Rodgers Creek, Greenville, and Concord-Green Valley faults.

“The 1906 quake happened when there were fewer people, and the area was much less developed,” said Schwartz. “The earthquake had the beneficial effect of releasing the plate boundary stress and relaxing the crust, ushering in a period of low level earthquake activity.”

The earthquake cycle reflects the accumulation of stress, its release as slip on a fault or a set of faults, and its re-accumulation and re-release. The San Francisco Bay Area has not experienced a full earthquake cycle since its been occupied by people who have reported earthquake activity, either through written records or instrumentation. Founded in 1776, the Mission Dolores and the Presidio in San Francisco kept records of felt earthquakes and earthquake damage, marking the starting point for the historic earthquake record for the region.

“We are looking back at the past to get a more reasonable view of what’s going to happen decades down the road,” said Schwartz. “The only way to get a long history is to do these paleoseismic studies, which can help construct the rupture histories of the faults and the region. We are trying to see what went on and understand the uncertainties for the Bay Area.”

Schwartz and colleagues excavated trenches across faults, observing past surface ruptures from the most recent earthquakes on the major faults in the area. Radiocarbon dating of detrital charcoal and the presence of non-native pollen established the dates of paleoearthquakes, expanding the span of information of large events back to 1600.

The trenching studies suggest that between 1690 and the founding of the Mission Dolores and Presidio in 1776, a cluster of earthquakes ranging from magnitude 6.6 to 7.8 occurred on the Hayward fault (north and south segments), San Andreas fault (North Coast and San Juan Bautista segments), northern Calaveras fault, Rodgers Creek fault, and San Gregorio fault. There are no paleoearthquake data for the Greenville fault or northern extension of the Concord-Green Valley fault during this time interval.

“What the cluster of earthquakes did in our calculations was to release an amount of energy somewhat comparable to the amount released in the crust by the 1906 quake,” said Schwartz.

As stress on the region accumulates, the authors see at least two modes of energy release – one is a great earthquake and other is a cluster of large earthquakes. The probability for how the system will rupture is spread out over all faults in the region, making a cluster of large earthquakes more likely than a single great earthquake.

“Everybody is still thinking about a repeat of the 1906 quake,” said Schwartz. “It’s one thing to have a 1906-like earthquake where seismic activity is shut off, and we slide through the next 110 years in relative quiet. But what happens if every five years we get a magnitude 6.8 or 7.2? That’s not outside the realm of possibility.”

The next ‘Big One’ for the Bay Area may be a cluster of major quakes

A cluster of closely timed earthquakes over 100 years in the 17th and 18th centuries released as much accumulated stress on San Francisco Bay Area’s major faults as the Great 1906 San Francisco earthquake, suggesting two possible scenarios for the next “Big One” for the region, according to new research published by the Bulletin of the Seismological Society of America (BSSA).

“The plates are moving,” said David Schwartz, a geologist with the U.S. Geological Survey and co-author of the study. “The stress is re-accumulating, and all of these faults have to catch up. How are they going to catch up?”

The San Francisco Bay Region (SFBR) is considered within the boundary between the Pacific and North American plates. Energy released during its earthquake cycle occurs along the region’s principal faults: the San Andreas, San Gregorio, Calaveras, Hayward-Rodgers Creek, Greenville, and Concord-Green Valley faults.

“The 1906 quake happened when there were fewer people, and the area was much less developed,” said Schwartz. “The earthquake had the beneficial effect of releasing the plate boundary stress and relaxing the crust, ushering in a period of low level earthquake activity.”

The earthquake cycle reflects the accumulation of stress, its release as slip on a fault or a set of faults, and its re-accumulation and re-release. The San Francisco Bay Area has not experienced a full earthquake cycle since its been occupied by people who have reported earthquake activity, either through written records or instrumentation. Founded in 1776, the Mission Dolores and the Presidio in San Francisco kept records of felt earthquakes and earthquake damage, marking the starting point for the historic earthquake record for the region.

“We are looking back at the past to get a more reasonable view of what’s going to happen decades down the road,” said Schwartz. “The only way to get a long history is to do these paleoseismic studies, which can help construct the rupture histories of the faults and the region. We are trying to see what went on and understand the uncertainties for the Bay Area.”

Schwartz and colleagues excavated trenches across faults, observing past surface ruptures from the most recent earthquakes on the major faults in the area. Radiocarbon dating of detrital charcoal and the presence of non-native pollen established the dates of paleoearthquakes, expanding the span of information of large events back to 1600.

The trenching studies suggest that between 1690 and the founding of the Mission Dolores and Presidio in 1776, a cluster of earthquakes ranging from magnitude 6.6 to 7.8 occurred on the Hayward fault (north and south segments), San Andreas fault (North Coast and San Juan Bautista segments), northern Calaveras fault, Rodgers Creek fault, and San Gregorio fault. There are no paleoearthquake data for the Greenville fault or northern extension of the Concord-Green Valley fault during this time interval.

“What the cluster of earthquakes did in our calculations was to release an amount of energy somewhat comparable to the amount released in the crust by the 1906 quake,” said Schwartz.

As stress on the region accumulates, the authors see at least two modes of energy release – one is a great earthquake and other is a cluster of large earthquakes. The probability for how the system will rupture is spread out over all faults in the region, making a cluster of large earthquakes more likely than a single great earthquake.

“Everybody is still thinking about a repeat of the 1906 quake,” said Schwartz. “It’s one thing to have a 1906-like earthquake where seismic activity is shut off, and we slide through the next 110 years in relative quiet. But what happens if every five years we get a magnitude 6.8 or 7.2? That’s not outside the realm of possibility.”

Network for tracking earthquakes exposes glacier activity

Alaska’s seismic network records thousands of quakes produced by glaciers, capturing valuable data that scientists could use to better understand their behavior, but instead their seismic signals are set aside as oddities. The current earthquake monitoring system could be “tweaked” to target the dynamic movement of the state’s glaciers, suggests State Seismologist Michael West, who will present his research today at the annual meeting of the Seismological Society of America (SSA).

“In Alaska, these glacial events have been largely treated as a curiosity, a by-product of earthquake monitoring,” said West, director of the Alaska Earthquake Center, which is responsible for detecting and reporting seismic activity across Alaska.

The Alaska seismic network was upgraded in 2007-08, improving its ability to record and track glacial events. “As we look across Alaska’s glacial landscape and comb through the seismic record, there are thousands of these glacial events. We see patterns in the recorded data that raise some interesting questions about the glaciers,” said West.

As a glacier loses large pieces of ice on its leading edge, a process called calving, the Alaska Earthquake Center’s monitoring system automatically records the event as an earthquake. Analysts filter out these signals in order to have a clear record of earthquake activity for the region. In the discarded data, West sees opportunity.

“We have amassed a large record of glacial events by accident,” said West. “The seismic network can act as an objective tool for monitoring glaciers, operating 24/7 and creating a data flow that can alert us to dynamic changes in the glaciers as they are happening.” It’s when a glacier is perturbed or changing in some way, says West, that the scientific community can learn the most.

Since 2007, the Alaska Earthquake Center has recorded more than 2800 glacial events along 600 km of Alaska’s coastal mountains. The equivalent earthquake sizes for these events range from about 1 to 3 on the local magnitude scale. While calving accounts for a significant number of the recorded quakes, each glacier’s terminus – the end of any glacier where the ice meets the ocean – behaves differently. Seasonal variations in weather cause glaciers to move faster or slower, creating an expected seasonal cycle in seismic activity. But West and his colleagues have found surprises, too.

In mid-August 2010, the Columbia Glacier’s seismic activity changed radically from being relatively quiet to noisy, producing some 400 quakes to date. These types of signals from the Columbia Glacier have been documented every single month since August 2010, about the time when the Columbia terminus became grounded on sill, stalling its multi-year retreat.

That experience highlighted for West the value of the accidental data trove collected by the Alaska Earthquake Center. “The seismic network is blind to the cause of the seismic events, cataloguing observations that can then be validated,” said West, who suggests the data may add value to ongoing field studies in Alaska.

Many studies of Alaska’s glaciers have focused on single glacier analyses with dedicated field campaigns over short periods of time and have not tracked the entire glacier complex over the course of years. West suggests leveraging the data stream may help the scientific community observe the entire glacier complex in action or highlight in real time where scientists could look to catch changes in a glacier.

“This is low-hanging fruit,” said West of the scientific advances waiting to be gleaned from the data.

Network for tracking earthquakes exposes glacier activity

Alaska’s seismic network records thousands of quakes produced by glaciers, capturing valuable data that scientists could use to better understand their behavior, but instead their seismic signals are set aside as oddities. The current earthquake monitoring system could be “tweaked” to target the dynamic movement of the state’s glaciers, suggests State Seismologist Michael West, who will present his research today at the annual meeting of the Seismological Society of America (SSA).

“In Alaska, these glacial events have been largely treated as a curiosity, a by-product of earthquake monitoring,” said West, director of the Alaska Earthquake Center, which is responsible for detecting and reporting seismic activity across Alaska.

The Alaska seismic network was upgraded in 2007-08, improving its ability to record and track glacial events. “As we look across Alaska’s glacial landscape and comb through the seismic record, there are thousands of these glacial events. We see patterns in the recorded data that raise some interesting questions about the glaciers,” said West.

As a glacier loses large pieces of ice on its leading edge, a process called calving, the Alaska Earthquake Center’s monitoring system automatically records the event as an earthquake. Analysts filter out these signals in order to have a clear record of earthquake activity for the region. In the discarded data, West sees opportunity.

“We have amassed a large record of glacial events by accident,” said West. “The seismic network can act as an objective tool for monitoring glaciers, operating 24/7 and creating a data flow that can alert us to dynamic changes in the glaciers as they are happening.” It’s when a glacier is perturbed or changing in some way, says West, that the scientific community can learn the most.

Since 2007, the Alaska Earthquake Center has recorded more than 2800 glacial events along 600 km of Alaska’s coastal mountains. The equivalent earthquake sizes for these events range from about 1 to 3 on the local magnitude scale. While calving accounts for a significant number of the recorded quakes, each glacier’s terminus – the end of any glacier where the ice meets the ocean – behaves differently. Seasonal variations in weather cause glaciers to move faster or slower, creating an expected seasonal cycle in seismic activity. But West and his colleagues have found surprises, too.

In mid-August 2010, the Columbia Glacier’s seismic activity changed radically from being relatively quiet to noisy, producing some 400 quakes to date. These types of signals from the Columbia Glacier have been documented every single month since August 2010, about the time when the Columbia terminus became grounded on sill, stalling its multi-year retreat.

That experience highlighted for West the value of the accidental data trove collected by the Alaska Earthquake Center. “The seismic network is blind to the cause of the seismic events, cataloguing observations that can then be validated,” said West, who suggests the data may add value to ongoing field studies in Alaska.

Many studies of Alaska’s glaciers have focused on single glacier analyses with dedicated field campaigns over short periods of time and have not tracked the entire glacier complex over the course of years. West suggests leveraging the data stream may help the scientific community observe the entire glacier complex in action or highlight in real time where scientists could look to catch changes in a glacier.

“This is low-hanging fruit,” said West of the scientific advances waiting to be gleaned from the data.

Dynamic stressing of a global system of faults results in rare seismic silence

In the global aftershock zone that followed the major April 2012 Indian Ocean earthquake, seismologists noticed an unusual pattern – a dynamic “stress shadow,” or period of seismic silence when some faults near failure were temporarily rendered incapable of a large rupture.

The magnitude (M) 8.6 earthquake, a strike-slip event at intraoceanic tectonic plates, caused global seismic rates of M≥4.5 to spike for several days, even at distances tens of thousands of kilometers from the mainshock site. But beginning two weeks after the mainshock, the rate of M≥6.5 seismic activity subsequently dropped to zero for the next 95 days.

Why did this rare period of quiet occur?

In a paper published today in the Bulletin of the Seismological Society of America (BSSA), Fred Pollitz of the U.S. Geological Survey and co-authors suggests that the Indian Ocean earthquake caused short-term dynamic stressing of a global system of faults. Across the planet, there are faults that are “close to failure” and ready to rupture. It may be, suggests Pollitz and his colleagues, that a large quake encourages short-term triggering of these close-to-failure faults but also relieves some of the stress that has built up along these faults. Large magnitude events would not occur until tectonic movement loads stress back on to the faults at the ready-to-fail levels they reached before the main shock.

Using a statistical model of global seismicity, Pollitz and his colleagues show that a transient seismic perturbation of the size of the April 2012 global aftershock would inhibit rupture in 88 percent of their possible M≥6.5 earthquake fault sources over the next 95 days, regardless of how close they were to failure beforehand.

This surprising finding, say the authors, challenges the previously held notion that dynamic stresses can only increase earthquake rates rather than inhibit them. But there are still mysteries about this process; for example, the global rate of M≥4.5 and M≥5.5 shocks did not decrease along with the larger shocks.

Dynamic stressing of a global system of faults results in rare seismic silence

In the global aftershock zone that followed the major April 2012 Indian Ocean earthquake, seismologists noticed an unusual pattern – a dynamic “stress shadow,” or period of seismic silence when some faults near failure were temporarily rendered incapable of a large rupture.

The magnitude (M) 8.6 earthquake, a strike-slip event at intraoceanic tectonic plates, caused global seismic rates of M≥4.5 to spike for several days, even at distances tens of thousands of kilometers from the mainshock site. But beginning two weeks after the mainshock, the rate of M≥6.5 seismic activity subsequently dropped to zero for the next 95 days.

Why did this rare period of quiet occur?

In a paper published today in the Bulletin of the Seismological Society of America (BSSA), Fred Pollitz of the U.S. Geological Survey and co-authors suggests that the Indian Ocean earthquake caused short-term dynamic stressing of a global system of faults. Across the planet, there are faults that are “close to failure” and ready to rupture. It may be, suggests Pollitz and his colleagues, that a large quake encourages short-term triggering of these close-to-failure faults but also relieves some of the stress that has built up along these faults. Large magnitude events would not occur until tectonic movement loads stress back on to the faults at the ready-to-fail levels they reached before the main shock.

Using a statistical model of global seismicity, Pollitz and his colleagues show that a transient seismic perturbation of the size of the April 2012 global aftershock would inhibit rupture in 88 percent of their possible M≥6.5 earthquake fault sources over the next 95 days, regardless of how close they were to failure beforehand.

This surprising finding, say the authors, challenges the previously held notion that dynamic stresses can only increase earthquake rates rather than inhibit them. But there are still mysteries about this process; for example, the global rate of M≥4.5 and M≥5.5 shocks did not decrease along with the larger shocks.

Researchers find existence of large, deep magma chamber below Kilauea volcano

A new study led by scientists at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science uncovered a previously unknown magma chamber deep below the most active volcano in the world – Kilauea. This is the first geophysical observation that large magma chambers exist in the deeper parts of the volcano system.

Scientists analyzed the seismic waves that travel through the volcano to understand the internal structure of the volcanic system. Using the seismic data, the researchers developed a three-dimensional velocity model of a magma anomaly to determine the size, depth and composition of the lava chamber, which is several kilometers in diameter and located at a depth of 8-11 km (5 – 6.8 miles).

“It was known before that Kilauea had small, shallow magma chambers,” said Guoqing Lin, UM Rosenstiel School assistant professor of geology and geophysics and lead author of the study. “This study is the first geophysical observation that large magma chambers exist in the deep oceanic crust below.”

The study also showed that the deep chamber is composed of “magma mush,” a mixture of 10-percent magma and 90-percent rock. The crustal magma reservoir below Kilauea is similar to those widely observed beneath volcanoes located at mid-ocean ridge.

“Understanding these magma bodies are a high priority because of the hazard posed by the volcano,” said Falk Amelung, co-author and professor of geology and geophysics at the UM Rosenstiel School. “Kilauea volcano produces many small earthquakes and paying particular attention to new seismic activity near this body will help us to better understand where future lava eruptions will come from.”

Scientists are still unraveling the mysteries of the deep internal network of magma chambers and lava tubes of Kilauea, which has been in continuous eruption for more than 30 years and is currently the most active volcano in the world

Researchers find existence of large, deep magma chamber below Kilauea volcano

A new study led by scientists at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science uncovered a previously unknown magma chamber deep below the most active volcano in the world – Kilauea. This is the first geophysical observation that large magma chambers exist in the deeper parts of the volcano system.

Scientists analyzed the seismic waves that travel through the volcano to understand the internal structure of the volcanic system. Using the seismic data, the researchers developed a three-dimensional velocity model of a magma anomaly to determine the size, depth and composition of the lava chamber, which is several kilometers in diameter and located at a depth of 8-11 km (5 – 6.8 miles).

“It was known before that Kilauea had small, shallow magma chambers,” said Guoqing Lin, UM Rosenstiel School assistant professor of geology and geophysics and lead author of the study. “This study is the first geophysical observation that large magma chambers exist in the deep oceanic crust below.”

The study also showed that the deep chamber is composed of “magma mush,” a mixture of 10-percent magma and 90-percent rock. The crustal magma reservoir below Kilauea is similar to those widely observed beneath volcanoes located at mid-ocean ridge.

“Understanding these magma bodies are a high priority because of the hazard posed by the volcano,” said Falk Amelung, co-author and professor of geology and geophysics at the UM Rosenstiel School. “Kilauea volcano produces many small earthquakes and paying particular attention to new seismic activity near this body will help us to better understand where future lava eruptions will come from.”

Scientists are still unraveling the mysteries of the deep internal network of magma chambers and lava tubes of Kilauea, which has been in continuous eruption for more than 30 years and is currently the most active volcano in the world

Mega-landslide in giant Utah copper mine may have triggered earthquakes

This is Figure 1 from K.L. Pankow et al. of megalandslide at the Bingham Canyon Mine, Utah. Landslide image copyright Kennecott Utah Copper. -  Seismic/Infrasound image by K.L. Pankow et al. Landslide image copyright Kennecott Utah Copper.
This is Figure 1 from K.L. Pankow et al. of megalandslide at the Bingham Canyon Mine, Utah. Landslide image copyright Kennecott Utah Copper. – Seismic/Infrasound image by K.L. Pankow et al. Landslide image copyright Kennecott Utah Copper.

Landslides are one of the most hazardous aspects of our planet, causing billions of dollars in damage and thousands of deaths each year. Most large landslides strike with little warning — and thus geologists do not often have the ability to collect important data that can be used to better understand the behavior of these dangerous events. The 10 April 2013 collapse at Kennecott’s Bingham Canyon open-pit copper mine in Utah is an important exception.

Careful and constant monitoring of the conditions of the Bingham Canyon mine identified slow ground displacement prior to the landslide. This allowed the successful evacuation of the mine area prior to the landslide and also alerted geologists at the University of Utah to enable them to successfully monitor and study this unique event.

The landslide — the largest non-volcanic landslide in the recorded history of North America — took place during two episodes of collapse, each lasting less than two minutes. During these events about 65 million cubic meters of rock — with a total mass of 165 million tons — collapsed and slid nearly 3 km (1.8 miles) into the open pit floor.

In the January 2014 issue of GSA Today, University of Utah geologists, led by Dr. Kristine Pankow, report the initial findings of their study of the seismic and sound-waves generated by this massive mega-landslide. Pankow and her colleagues found that the landslide generated seismic waves that were recorded by both nearby seismic instruments, but also instruments located over 400 km from the mine. Examining the details of these seismic signals, they found that each of the two landslide events produced seismic waves equivalent to a magnitude 2 to 3 earthquake.

Interestingly, while there were no measurable seismic events prior to the start of the landslide, the team did measure up to 16 different seismic events with characteristics very much like normal “tectonic” earthquakes beneath the mine. These small (magnitude less than 2) earthquakes happened over a span of 10 days following the massive landslide and appear to be a rare case of seismic activity triggered by a landslide, rather than the more common case where an earthquake serves as the trigger to the landslide.

Later studies of both the seismic and sound waves produced by this landslide will allow Pankow and her team to characterize the failure and displacement of the landslide material in much more detail.

Mega-landslide in giant Utah copper mine may have triggered earthquakes

This is Figure 1 from K.L. Pankow et al. of megalandslide at the Bingham Canyon Mine, Utah. Landslide image copyright Kennecott Utah Copper. -  Seismic/Infrasound image by K.L. Pankow et al. Landslide image copyright Kennecott Utah Copper.
This is Figure 1 from K.L. Pankow et al. of megalandslide at the Bingham Canyon Mine, Utah. Landslide image copyright Kennecott Utah Copper. – Seismic/Infrasound image by K.L. Pankow et al. Landslide image copyright Kennecott Utah Copper.

Landslides are one of the most hazardous aspects of our planet, causing billions of dollars in damage and thousands of deaths each year. Most large landslides strike with little warning — and thus geologists do not often have the ability to collect important data that can be used to better understand the behavior of these dangerous events. The 10 April 2013 collapse at Kennecott’s Bingham Canyon open-pit copper mine in Utah is an important exception.

Careful and constant monitoring of the conditions of the Bingham Canyon mine identified slow ground displacement prior to the landslide. This allowed the successful evacuation of the mine area prior to the landslide and also alerted geologists at the University of Utah to enable them to successfully monitor and study this unique event.

The landslide — the largest non-volcanic landslide in the recorded history of North America — took place during two episodes of collapse, each lasting less than two minutes. During these events about 65 million cubic meters of rock — with a total mass of 165 million tons — collapsed and slid nearly 3 km (1.8 miles) into the open pit floor.

In the January 2014 issue of GSA Today, University of Utah geologists, led by Dr. Kristine Pankow, report the initial findings of their study of the seismic and sound-waves generated by this massive mega-landslide. Pankow and her colleagues found that the landslide generated seismic waves that were recorded by both nearby seismic instruments, but also instruments located over 400 km from the mine. Examining the details of these seismic signals, they found that each of the two landslide events produced seismic waves equivalent to a magnitude 2 to 3 earthquake.

Interestingly, while there were no measurable seismic events prior to the start of the landslide, the team did measure up to 16 different seismic events with characteristics very much like normal “tectonic” earthquakes beneath the mine. These small (magnitude less than 2) earthquakes happened over a span of 10 days following the massive landslide and appear to be a rare case of seismic activity triggered by a landslide, rather than the more common case where an earthquake serves as the trigger to the landslide.

Later studies of both the seismic and sound waves produced by this landslide will allow Pankow and her team to characterize the failure and displacement of the landslide material in much more detail.